Ever purchase a locomotive or 85’ passenger car advertised by the manufacturer to run on 18” curves only to find it regularly derails on 20, 24 or even 26” curves?
It’s happened to me. So the question is what’s a produt’s real minimum radius? How do manufacturers come up with the number?
When I was working in communications and electronics I figured specs were placed on a dart board and the one in charge was blind folded and tossed darts for each product.
Mel
Modeling the early to mid 1950s SP in HO scale since 1951
My Model Railroad
http://melvineperry.blogspot.com/
Bakersfield, California
I’m beginning to realize that aging is not for wimps.
LOL I think you may be right Mel!
Clearly there is a problem but whats a good rule to follow? If they say 18 make it 28? If they say 22 make it 32?
Here is a good rule of thumb for rolling stock,
3 times the truck centers = minimum radius
85’ long pasenger car, about 10" truck centers, 30" radius.
40’ box car, 5" truck centers, 15" radius.
For steam locos,
10-12 times the rigid driver wheel base.
Typical 2-8-2, 2.25" wheelbase, 22" radius.
your mileage may vary…
Sheldon
Advertised to operate on 18" has implied conditions with it, namely ideal track, “reasonable” operating speed, and the rolling stock is in proper operating condition.
In your specific case, have you made absolutely certain that it’s not YOUR fault? Is your trackwork up to snuff? Your mention of derailing on your 24" or 26" curves makes me question your trackwork. Not to imply you have totally crappy trackwork, but it might be something very tiny and not obvious. Even a speck of ballast. My skepticism is not without merit because just this week we had some fellow on this forum who had a similar situation, and turns out it was his fault.
Second, did you make sure the car’s wheels are in gauge, AND, if in gauge, are not shifted on the axle a different amount? Make sure the truck screws are adjusted proper tension. The manufacturers test their m.o.r. using ideal samples, but we all know that production items are often less-than-perfect out of the box. Unfortunate, but true. Often (usually?) need tweaks.
Third, what speed are you operating? Model Passenger trains can’t really handle higher end prototype operating speeds, especially at curves.
Only then, after these more expected problems are ruled out should we begin to question if an item is incorrectly designed. This is NOT intended to give model train manufacturers a pass, but I’ve seen a lot of knee-jerk reactions from model railroaders to know we are quick to blame others before looking at our own faults. Especially when it comes to t
Thanks Sheldon, now why isn’t that in the “How to be a Model Railroader” book? [:P]
Expressed somewhat differently, similar recommendations are in the NMRA publications…have been for 50 years or more…
Sheldon
Here’s the specific “humble pie” incident I refer to:
"Here I go again. Looking for help when I can’t figure it out. All my locos steem and diesel, 2-8-2’s, 4-6-2’s, 4 axle, 6 axle and 80’ passenger cars run smoth through this 26” curve but a 4 axle RDC gets to one point of the curve and it slows - sounds like grinding and then proceeds through, If I run oit at a slow speed to gets stuck. I can move it with my hand through the curve and don’t feel any resistance.
Ideas??"
LATER:
"SOLVED !!!
There was a track nail sitting a little too high (not snug to the tie). I crawled under the layout, Removed a cross member of the benchwork (temporary) and created a access point. Not easy for an old man. Then I slowly ran the loco until it stopped. With my hand I moved the loco and could hear something grinding. Nothing visible arround the loco but underneath I found this nail.
It was painted so I never would have seen it unless I was right on top of the track. Lifting up the loco i could see slight scratches on one of the underside details.
I don’t understand why the loco caught this nail in only one direction but now it works.
Next step is to re-install the scenery partition and finish the tunnel portal.
So getting back to the OP’s dilmemma, why don’t locomotives and passenger cars operate on the advertised minimum radius?
Shouldn’t they?
Aside from that, many people, like with computers, expect things to work well at minimum specs, which never seems like a good idea, trains or computers.
Yes, they darned well should. But…nothing we handle in the hobby, except for tracks and ground foam, and I guess adhesives, are mass produced. They are hand assembled, meaning the variance is quite high in fit and finish. I purchased that four-pack Spectrum heavyweight passenger car in Pennsy livery that some of you know…maybe too well. I had to order the under/over shank Kadee couplers so that they would couple to each other. Four cars, same supplier, same importer, same style, and no three of them would shake hands. And these were Spectrum!
Walthers used to advertise that their heavies were suitable on 24" curves. Nyuh-uuuhh! Not even close. I was pretty good at laying 24" curves on my second layout when I purchased them. I found out the hard way that backing those cars through pristine 24" curves was a pipe dream.
Then some of you may recall my foray into curved #7.5 Code 93 Walthers/Shinohara turnouts on that same construction. What a nightmare.
Soooo…yes, I think they should all be more careful about their specs. However, there is so much human activity in our hobby on both sides of the ocean, shipper and user, that it’s a lot of trail and error at times. We know my curves weren’t really ‘pristine’…at all. They were close, but they weren’t consistent through their arc. It wasn’t until I got them out to 27+" that I had consistently reliable rolling characteristics in both directions. Was it me? The way the diaphragms worked? The way they were attached to each rolling item? It was all of it.
I put all of this into the same category as the dealer response to those EPA stickers on new cars: Your Mileage May Vary.
Robert
OK, if you really want to understand what goes on when your train goes around a curve, here is some light reading:
http://webspace.webring.com/people/ib/budb3/arts/tech/curv.html
The website this info comes from is full of detailed technical info about model trains:
http://webspace.webring.com/people/ib/budb3/index.html
Sheldon
Selector,
Those Bachmann heavyweights, from nearly 20 years ago, did not have the best coupler mounting system.
But just like this thread, they refected the endless desire to make scale models g
I think the biggest factor in the minimum radius game is speed. The manufacturers are trying to market to the largest possible base. Therefore, “minimum radius” is a more desirable advertising metric than “desirable radius.” More folks have minimum 22’s Than 32’s +, so they tell us it will work on a 22. It’s not deceptive advertising, it’s just marketing. It will work on a 22—at 10% throttle. For mainline passenger speed, it will need something significantly wider.
My minimum radius is 26, most are 30, but I like those big articulated steamers, so I’m willing to slow them down to navigate that 26” curve.
Read literally, if a manufacturer claims a passenger car will run on 18" radius curves that means, as I read it, only that if you put the car on a curve of that radius you can push it around the curve and it won’t derail. Will two such cars coupled together still run on that 18" radius curve? They don’t claim any such thing when they boast of an 18" minimum radius.
In practical operation, what is it coupled to? Many locomotives, particularly with body mounted couplers, have a coupler swing that effectively increases the minimum radius of whatever it is they are coupled to, sometimes considerably. So what you really need to know is, what is the effective and practical minimum radius of the locomotive and car(s) you intend to run? And not shockingly, no manufacturer can presume to guess what that is.
In short, 18" radius for the car alone, perhaps … but so what? It is going to be coupled to something. And that changes everything.
Dave Nelson
Like I thought I implied, they mostly do. As long as they’re given a chance to, with decent track, in proper condition, and at reasonable speeds.
Well stated, Dave. There is no “official” definition of what the claim means, so it’s indeed open to interpretation. I tend to read such claims with a grain of salt, as I do ANY claim that ANY business makes these days. Often a matter of Ideal conditions versus reality. You know any manufacturer will stretch a product claim as far as they can legally go, and then often push the boundaries beyond legal. Prime example these days is the term “natural” food, which people assume means something but it doesn’t. As Dave says, a car said to “operate on 18” curves", has no strict agreed-upon conditions, nor guarantees about how well it will operate or how good (or terrible) it will look. I tend to think of the 18" claim in minimalist terms, that I could put the single car alone on the track and push it by hand, slowly. Beyond that, thou
I bought a set of Rivarossi coaches advertised to run on 18 inch curves. They did. But I quickly found out they would not run on 17 15/16 curves. I relaid one arc of track to bring it up to 18 and they worked fine.
Well, fellas, why bother putting a coupler on two ends of a passenger car rated for 24" radius if you can’t expect to run them…ummmm…you know…
Sheldon, I like the cars and have enjoyed them. Dispite my dismay at my initial impression of them once I tried to trail all four behind my K4, I thought enough of them to order the fix-me couplers and get them to work. In fact, I have never encountered another problem since replacing two of those couplers, the ones that sagged the worst.
As for the Walthers cars, I based my yard curves on their stated ‘facts’. Silly me. Just like I was silly to swallow their claims for their curved #7.5 unchewed. In any case, it was just shoving them in the yard throat where I sometimes had a derailment…sometimes as in about 70% of the time. Out on the mains, my minimum curves were 28" with the outside main being 46".
-Crandell
Bubbytrains, That guy may very well have been me! I had an RDC stalling at a certain point on a curve. Turned out to be a nail.
I never run my trains more than 40 SMPH, most run slower.
The cars that derailed for ME were a tandem BLI coach and a 6 axle diesel.
I have to say that you are correct! 90% of the time it’s trackwork.
The reason for the post is I have seen others have the same problem and I thought I would put the question out there. So far, there have some very useful replies.